Graph of the Day: Freeze-up and Ice-out Dates for Vermont Ponds, 1970-2010
This paper explores how climate change has affected Vermont in recent decades using long-term datasets: specifically the impact on freeze dates, the length of the growing season, the frozen duration of its small lakes, and the onset of spring. The freeze period in Vermont has got shorter, and the growing season for frost-sensitive plants has got longer by about 3.2 (±0.9) days per decade; as the last spring freeze has come earlier by 1.4 (±0.7) days per decade and the first autumn freeze has come later by 1.8 (±0.6) days per decade. The frozen duration for small lakes, for which freeze-up and ice-out depend on mean temperatures over longer periods has been changing at roughly double this rate. Over the past forty years, ice-out has got earlier by 2.9 (±1.0) days per decade and freeze-up has occurred later by 3.9 (±1.1) days per decade, so that the frozen duration in winter has decreased by 6.9 (±1.5) days per decade. The first leaf of Vermont lilacs, an indicator of early spring, is closely correlated with the ice-out of our two small reference lakes. Lilac first leaf has also been coming earlier by 2.9 (±0.8) days per decade, while lilac first bloom has advanced more slowly by 1.6 (±0.6) days per decade. The means that in the past forty years, the growing season for frost-sensitive plants has increased by almost 2 weeks; and for frost-hardy plants the growing season may have increased by as much as three to four weeks.
